Twin girls: alliteration, matchy, MN, HELP!

I'm pregnant with twin girls (our first!). DH and I have spent a long time discussing names and we've settled on Marina and Luna. Both names are meaningful to us, and I love how the meanings of moon and sea are so intimately connected, in literature, mythology, and nature: how the moon pulls the tides and the sea follows the moon. I hope my daughters are as close as the moon and the sea.

I need y'alls advice on sorting out middle names! I have absolutely fallen in LOVE with the combo Marina Mayla. I'm not sure of the origins of Mayla, but for various reasons it is meaningful to DH and me. As soon as that name popped into my head, I immediately thought of LunaLyra. Lyra is the main character in a book series I adored as a kid; I love its sound; and I love the associations with music and stars.

However, I am concerned that LunaLyra sounds too sing-songy. I was considering adding a second MN, such as: Marina Mayla Jane and LunaLyraBelle (purely for flow). I feel like I want to add a syllable btw Luna and Lyra (Marina and Mayla, at least, are different #s of syllables), as in LunaBelleLyra. (Does LunaBelle sound too much like a cow?) But my concern is that adding a name between Luna and Lyra breaks up the pattern.

So I guess my questions are these:
1. Are the names Marina and Luna too matchy? Is the connection too obvious?
2. Is Marina Mayla too sing-songy? How about LunaLyra? Taken together, as names for twins, is that too much alliteration? (I kind of like having the alliteration for them both).
3. If you think those combos are too sing-songy, what could I do to break them up? What are some ways to make Luna two syllables, either longer forms of one name or combos like LunaDay or LunaBea or Luna __.
4. What if I did MarinaLyra and Luna Mayla?
5. Am I crazy?

Answer those questions, or ignore them completely and give me other feedback! Honest opinions appreciated, I will not be offended, I promise

I am a big fan of alliteration, if I had twin girls they'd be MelodyMarie and GeorginaGrace. But I think flow is important and I'm sorry but LunaLyra lacks it completely, the fact that the names begin with the same letter, have the same amount of letters, end with the same letter, and have the same amount of syllables all work against them together as a combo. What about another L names with more/less syllables than Lyra? Louisa, Lisabeth, Lillian, Liliana, Leigh,? You're not crazy, and I think the Marina and Luna sound lovely as twins